The Michelle story is bait for the base— to get Joe out. Who it is that comes in, to these desperate , is almost secondary.
Kamala must be the interim, but the Democrat Convention decides the nominee and Kamala isn’t it, apparently.
As for Michelle, she could then decline the nomination at the Convention and let the runner-up take the nomination, or whoever.
I’m afraid this is a contingency plan that has been in the works and only appears to be chaos, only to justify their maneuvers in play. That pesky Constitution has to be satisfied, or “appear” to be. 😬